For an object which is a reference to an object in some source,
this holds the reference to the source object,
so that should the reference have to be de-referenced,
then we know where to go and get the info.

Releases ALL of the memory used by this indirect object,
and all of its component/child objects.
This method is called automatically by 'PDF::API2::Basic::PDF::File->release' (so you don't have to call it yourself).

NOTE,
that it is important that this method get called at some point prior to the actual destruction of the object.
Internally,
PDF files have an enormous amount of cross-references and this causes circular references within our own internal data structures.
Calling 'release()' forces these circular references to be cleaned up and the entire internal data structure purged.

Developer note: As part of the brute-force cleanup done here,
this method will throw a warning message whenever unexpected key values are found within the PDF::API2::Basic::PDF::Objind object.
This is done to help ensure that unexpected and unfreed values are brought to your attention,
so you can bug us to keep the module updated properly; otherwise the potential for memory leaks due to dangling circular references will exist.

This merges content information into an object reference place-holder.
This occurs when an object reference is read before the object definition and the information in the read data needs to be merged into the object place-holder

Returns a new copy of this object.
The object is assumed to be some kind of associative array and the copy is a deep copy for elements which are not PDF objects,
according to $pdf,
and shallow copy for those that are.
Notice that calling copy on an object forces at least a one level copy even if it is a PDF object.
The returned object loses its PDF object status though.

If $res is defined then the copy goes into that object rather than creating a new one.
It is up to the caller to bless $res,
etc.
Notice that elements from $self are not copied into $res if there is already an entry for them existing in $res.